Lake Beulah is a Marl Lake (and that's good!)

The lake is not like a bathtub. Sunken islands like this one in the middle of the Upper Lake, are just a few feet below the surface. Most don’t even know they are there, but they provide essential habitat for fish.

Consternation continues to build over the impact of wake boats on Lake Beulah. Recent photos like those in this article point to how wake boats, with their deep ‘prop wash’ can chew up the lake bottom, sometimes in surprising locations. A previous article in LAKE VIEWS pointed to research showing wake boat prop wash can extend to a depth of 30’ below the surface.

After a wake boat went over the sunken island, significant bottom disturbance can be seen.

Some are asking if this bottom disturbance is of any consequence, suggesting that the sediment stirred up simply resettles so that all is well. The answer is that while the sediment will resettle, a critically important component of the sediment is literally destroyed.

This critically important component of the lake bottom is called marl, a calcium carbonate or limerich mudstone that plays a significant role in the ecology of freshwater lakes like Lake Beulah.

A long stretch of the bottom shows scaring where bottom algae once flourished.

Calcium concentrations in the lake are so important that scientists have been continually measuring them as a critical factor in determining how the pumping of East Troy’s Well #7 may be impacting Lake Beulah water chemistry. I’m told these measurements, which have been ongoing since the 1990s, were finally stopped this year, the reason being the data is clear. But this article isn’t about the impact of the well, let that be for another time.

The message here is ‘Be glad Lake Beulah is a marl lake’. The presence of marl impacts the chemical composition, physical properties, and biological dynamics within the lake. Let’s take a quick look at each of these factors.

CHEMICAL COMPOSITION & WATER QUALITY

Bubbling up through the underground aquifer supplying water to Lake Beulah are ions of calcium and carbonate which enter the lake dissolved in groundwater. Once in the lake, these ions help maintain the alkalinity and pH levels of lake water.

A stable pH is crucial for the survival of many aquatic organisms, as drastic fluctuations can be harmful or even lethal to them. Accumulation of calcium-rich marl sediments creates habitat for the diverse aquatic life of Lake Beulah.

NUTRIENT CYCLING

Marl deposits impact nutrient cycling within the lake, particularly the cycling of phosphorus ions, the presence of which can be problematic to a clear, clean lake. In Lake Beulah, marl is formed when undesirable phosphorus binds with calcium carbonate from the aquifer and settles to the lake bottom, thus reducing available phosphorus in the water column. This is good because it can limit phosphorus-stimulated algal blooms which can over time lead to lake eutrophication. Eutrophication of the lake is bad because it depletes oxygen levels, causing dead zones where aquatic life cannot survive. By regulating phosphorus availability, marl helps to maintain a balanced ecosystem.

HABITAT AND PHYSICAL STRUCTURE

Marl deposits contribute to the physical structure of the lake bed. These deposits create unique microhabitats for various organisms. Bottom dwelling invertebrates, such as snails and insects, find refuge and breeding grounds in these marl-rich substrates. Additionally, the presence of marl can influence the type of vegetation that thrives in and around the lake.

Lake Beulah is home to a bottom algae called chara that prefers a calcium-rich environment. These plants, in turn, provide habitat and food for a variety of aquatic organisms, including fish. Unfortunately, anecdotal evidence points to a decline in the presence of chara at some spots on the lake.

BIOLOGICAL INTERACTIONS

Biological communities within marl-rich lakes like Lake Beulah can be distinct from those in other freshwater systems. Fish species, for example, may exhibit different feeding and spawning behaviors in these environments. The clear water typically associated with marl lakes, due to reduced algal growth, can affect predator-prey interactions. Visual predators, such as certain species of fish and birds, may find it easier to locate prey in these conditions.

CONCLUSION

In summary, marl significantly contributes to the ecology of Lake Beulah by influencing its water chemistry, nutrient cycling, habitat structure, and biological interactions. The presence of Marl helps to stabilize pH levels, regulate nutrient availability, create unique habitats, and shape biological communities.

The process of marl formation is extremely important in helping the lake maintain its clearwater status. Unfortunately, disturbance to bottom sediments quickly destroys marl by dissolving it, thereby releasing phosphorus back into the water.

Understanding the role of marl in Lake Beulah is essential for the conservation and management of the lake, ensuring it remains the vibrant and healthy ecosystem we have always known. Wake boaters, and those who choose to advocate for their continued use on Lake Beulah should ask themselves if the fun is worth the cost to the lake we all love.